Reversible stress and strain limits of the critical current of practical REBCO and BSCCO wires

Abstract

Practical REBCO and BSCCO-2223 tape-shaped wires are now manufactured on an industrial scale. They are a typical composite material consisting of superconducting layer/filaments together with functional components. These functional components affect directly the stress and strain dependences of the critical current. When applying an external stress R, the critical current Ic was measured. Then the external stress was reduced to R = 0 and the recovered critical current Icr was again measured. The tensile stress and strain dependences of both normalized critical currents divided by the original value, Ic/Ic0 and Icr/Ic0 were investigated. In general Icr/Ic0 recovered close to unity when the applied stress was low, but its recovering level decreased gradually with increasing applied stress. The definition of the reversible stress and strain limits was investigated and its validity was proved using the cyclic loading test. The original definition of reversible stress and strain limits of critical current relates to: (1) when releasing the applied stress and strain, the Ic shall recover to the original value, and (2) when applying the cyclic stresses, the Ic shall keep the original value. Here, as a practical definition for the reversible stress and strain limits, the tensile stress and strain at 99% recovery of Ic have been proposed. On the other hand, it was made clear that the stress and strain at Ic 95% retention are not valid for use commonly as a criterion of reversible stress and strain limits for both practical REBCO and BSCCO-2223 wires.